Thermal and abrasion resistant sintered alloy

ABSTRACT

An alloy prepared by adding 0.3 to 5 percent by weight of a ferrocarbide of an iron-carbon alloy containing one or more of carbide forming elements to a base comprising 0.6 to 2 percent of carbon, 0.5 to 5 percent of molybdenum, 6.0 to 15 percent of cobalt, 0.5 to 4 percent of nickel, by weight, and the balance iron and molding and sintering has large thermal resistance and abrasion resistance.

United States Patent Takahashi et al. Sept. 24, 1974 [5 THERMAL ANDABRASION RESISTANT 2,562,543 7/1951 Gippert 75/123 1( SINTERED ALLOY2,662,010 12/1953 Ahles 75/123] 3,471,343 10/1969 Koehler 75/125 [75]Inventors: Kenta ka y 3,495,957 2/1970 Matoba et a1 29/182.1

Minoru Hasegawa, Saitama; Kaoru Nara, Kawaguchi, all of Japan PrimaryExaminer-Benjamin R. Padgett [73] Asslgnee' $2232 22 Rmg AssistantExaminer-B. Hunt Attorney, Agent, or Firm-Sughrue, Rothwell, Mion, [22]Filed: Sept. 5, 1972 Zinn & Macpeak [21] Appl. No.1 286,392

[57] ABSTRACT [52] US. Cl 29/182, 29/182.l, 29/l56.7 A,

75 175 75 123 1 75 123 K An alloy prepared by adding 0.3 to 5 percent by[51] Int. Cl B221 l/00 Weight of a ferrocarbide of iron-carbon alloy[58] Field of Search 75/125, 123 J, 123 K; raining one or more ofcarbide forming elements to a 29/182.l, 182, 156,7 A base comprising 0.6to 2 percent of carbon, 0.5 to 5 percent of molybdenum, 6.0 to 15percent of cobalt, [56] Refer n e Cit d 0.5 to 4 percent of nickel, byweight, and the balance UNITED STATES PATENTS iron and molding andsintering has large thermal resis- 2,136,690 11/1938 Jardine 29/156.7 Atame and abraslo resstance' 1 Claim, 2 Drawing Figures PAIENTED8EP241974 I 3&3], 81:5

' I 0 EXAMPLE OF THIS INVENTION CONVENTIONAL SINTERED FERRO-ALLOY.

x CONVENTIONAL cAsT ALLOY 8 I 500 8 8 a 5 400- 300 z O E 5:: 200 \x\IOO- NgslgALlO 2'00 3OO 4OO sbo 6 00 IcI TRANSFORMATION TEMP.

FIG. 2

g 0 EXAMPLE OF THIS INVENTION E v CONVENTIONAL SINTERED FERRO-ALLOY Qx'cONVENTIONAL CAST ALLOY O: m 0.25- 1: LL O.20- o P O.I5- x O I- x g 0x 5/0 I AL IOO 2OO sOo 400 500 ("OI TRANSFORMATION TEMP.

THERMAL AND ABRASION RESISTANT SINTERED ALLOY BACKGROUND OF THEINVENTION A publicly known metal such as chromium, cobalt, tungsten,etc. has not only a large abrasion resistance but also is prominent inits characteristics at elevated temperatures and is applied in variousfields. However, such a metal has many problems to be solved when it isused as sintered parts for a machine. That is, such a metal has a highmelting point so that the sintering temperature is, of necessity,required to be elevated and the sintering time has to be extended, and,therefore, it is naturally disadvantageous in cost.

SUMMARY OF THE INVENTION The present invention provides a sintered alloyhaving large thermal resistance and abrasion resistance suitable for useas a sliding element such as, for example, a valve sheet, in which highthermal resistance and high abrasion resistance are required. That is,the present invention comprises a sintered thermal and abrasionresistant alloy comprising added 0.3 to percent by weight of aferro-carbide of an iron-carbon alloy containing one or more carbideforming elements to a base comprising, by weight, 0.6 to 2 percent ofcarbon, 0.5 to 5 percent of molybdenum, 6.0 to percent of cobalt, 0.5 to4 percent of nickel and the balance iron and molded and sintered.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the hardnessat elevated temperatures of sintered alloys of the Examples and of aconventional cast iron and sintered ferro alloy; and

FIG. 2 is a graph showing the abrasion resistance of sintered alloys ofthe Examples and of a conventional cast iron and a sintered ferro alloy.

DETAILED DESCRIPTION OF THE INVENTION In the sintered alloy of thepresent invention, carbon is solidified in an iron base to form a finepearlite structure and plays a large role in improving the strength ofthe alloy material, however, when the carbon content is less than 0.6percent, by weight, the alloy changes to a ferrite structure whichdecreases the hardness necessary for abrasion resistance, while, withmore than 2.0 percent of carbon, the alloy changes to acementiteexcessive structure which becomes unnecessarily high inhardness and increases in brittleness.

Molybdenum increases the tenacity of the alloy as well as the impactstrength and endurance limit, and, on the other hand, improves the heattreatment property and stabilizes the structure after sintering tocontribute to the thermal and abrasion resistance of alloy. However,there is little effect with less than 0.5 percent of molybdenum and evenif more than 5 percent is present, no increased effect corresponding tothe increase in level is obtained.

Nickel strengthens the base structure of the alloy and improves thethermal resistance and abrasion resistance. However, the effect is smallwith a nickel content of less than 1 percent, while, when it becomesmore than 4 percent, the base structure locally changes to martensite sothat the hardness increases unnecessarily.

Cobalt improves substantially the thermal resistance and abrasionresistance at elevated temperatures and has been established at 6 to 15percent on the basis of a synergistic effect with other elements.

The ferro-carbide is an iron-carbon alloy containing one or morecarbide-forming elements (for example, chromium, molybdenum, cobalt,tungsten, titanium, vanadium, boron, etc.) in a base and diffuses in thebase structure without being decomposed at the time of sintering toimprove the abrasion resistance of the alloy. However, with less than0.3 percent, the effect is not remarkable while, with more than 5percent, the hardness increases unnecessarily and the formability of thepowder is reduced and the strength is lowered.

The present invention will be further illustrated by the followingExamples by which the present invention is not intended to be limited.All percents are by weight.

EXAMPLE 1 0.7 percent of graphite powder (l00 mesh), 0.6 percent (asmolybdenum) of ferro-molybdenum powder mesh), 0.6 percent of carbonylnickel (-250 mesh), 6.5 percent of cobalt powder (150 mesh), 0.39percent of ferro-carbide powder (alloy powder comprising 3.25 percent ofcarbon, 39.0 percent of nickel, 29.0 percent of chromium, 15.5 percentof tungsten, 10.0 percent of cobalt, and the balance iron (150 mesh),and 1 percent of zinc stearate as a lubricant were added to reduced ironpowder (l00 mesh) and mixed and molded under a pressure of 6 ton/cm andsintered at l,120 to 1,170C for 30 to 60 minutes in an atmosphere ofdecomposed ammonium gas. The sintered material so obtained had a densityof 6.6 g/cm and a Rockwell B scale hardness of 91.

EXAMPLE 2 4.75 percent of ferro carbide powder (alloy powder comprising3.51 percent of carbon, 14.1 percent of chromium, 4.3 percent ofmolybdenum, 1.51 percent of vanadium, 1.97 percent of cobalt and thebalance iron (150 mesh) was added and a sintered material comprising1.76 percent of carbon, 4.62 percent of molybdenum, 3.82 percent ofnickel, 13.9 percent of cobalt and the balance iron was made under thesame conditions as described in Example 1. The sintered material soobtained had a density of 6.8 g/cm and a Rockwell B scale hardness of96.

To examine the abrasion resistance of the sintered alloys obtained inExamples 1 and 2, a hardness test at elevated temperatures and anabrasion test using a valve sheet abrasion testing machine (rotationnumber 3,000 rpm, spring pressure 35 Kg, valve velocity at the time ofvalve closing 0.5 m/sec., width of valve 1 mm, number of repeating test8 X 10 material SUH 31 B) were run. Incidentally, for comparison, thesame tests were run on a conventionally known cast iron and a sinteredferro alloy. In this case, the composition of cast iron and ferro alloywere as follows:

Sintered ferro alloy:

Carbon 1 percent, chromium 3 percent, copper 3 percent, the balanceiron.

Cast iron:

Carbon 3.02 percent, silicon 2.01 percent, manganese 0.48 percent,chromium 0.81 percent, the balance iron.

FIG. 1 shows the results of the measurement of the hardness at elevatedtemperatures of the sintered alloys in Examples 1 and 2 in comparisonwith a conventionally known cast iron and sintered ferro alloy. As isaptemperatures. Thus, the alloy of the present invention has largethermal resistance and abrasion resistance.

What is claimed is: 1. A thermal and abrasion resistant sintered alloyparent from FIG. 1, the sintered alloys in Examples 1 5 comprising amolded and sintered powdery composi and 2 are higher in hardness thanthe conventional cast iron and sintered ferro alloy and are excellent inhardness characteristics.

FIG. 2 shows the abrasion test results on the sintered alloys ofExamples 1 and 2 in comparison with a conventionally known cast iron andsintered ferro alloy. The sintered alloy of the present invention wasvery small in amount and abraded and stable at elevated nickel and thebalance iron.

UN Il EiD STATES PATENT OFFICE CE TIFI A E OF CORRECTION It; is,petrifiedxtfieti ei'i or"appears in the above-identified patent 'andthat said Letter Ife'ten't, are herebycorrected as shown below:

v In the eleilrhed-Priority Delta/was omitted. Should read:

4f Piiib 2 1 1972 p s ned;g d1$1ed this 19th day of November 1974.

(SEAL) Atteet:

McCOY- M.

c. I-'IARSHALL DAN? At-testing Officer Commissioner of- PatentsFORMPO-IOSO (10-69) I v oc 0315mm O us.sovrimmzwr rminms brncc: 859,930

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,:8 37 -,'8 I6 v Dated segtembej y 24, 1974 Inventor(s) I Tkaha-s hi at al Itis jcerti fied th gatjetrorappears in the above-identified patent 'andthat said Lettrs Patent are herebycorrected as shown below:

In the He adin g The 1a i1'1r1 e d Priority Datawaxs omitted. Shouldi'ead:

-Sign e'd atgfllfgaled' this 19th day of November 1974.

(SEAL)- Attest:

McCOY ft- G1B$QNJRQLA1 c. MARSHALL DANN Attestlng Officer Commissionerof Patents I 3" Po-wso (10-69) I I UscOMM-DC scan-ps9

